There are significant opportunities for developing low cost imaging modalities for localized cancer therapy monitoring and 2assessment which could serve to improve clinical outcomes. The principal hypothesis which underpins this project is that near-field microwave imaging can provide new forms of moderately-resolved (cm-scale) spatial information that will positively influence clinical decision making in the therapy setting. Testing this hypothesis is a long term commitment given the complexities associated with microwave imaging in tissues which requires both the development of a viable microwave imaging methodology and the accumulation of experimental evidence on the value of the information that can be recovered with microwave techniques. Our research plan not only focuses on critical technology developments but also seeks to establish the limits of microwave imaging performance in vivo under controlled conditions. The central themes of our proposed technology advances are twofold: (1) to develop 3D imaging methods at the laboratory scale and (2) to realize high quality imaging capabilities not dependent on saline bath immersion. The primary focus of our experimental effort is to deploy our existing 2D imaging approach in a series of in vivo animal studies where we investigate microwave imaging of (i) therapeutic temperature elevation, (ii) thermally-induced lesions and (iii) radiation- induced tissue reactions. The specific aims that will be pursued during the proposed project period are: (1) development of three-dimensional data acquisition hardware based on mechanical translation and limited-angle rotation of fixed arrays of transceiving elements, (2) development of a suite of three- dimensional image reconstruction algorithms which include the 3D analogs of the 2D image enhancement methods of dual meshing and total variation minimization, (3) evaluation and optimization of 3D microwave imaging using preclinical laboratory studies of increasing complexity with particular attention on improving data calibration and maximizing data-model match, (4) experimental evaluation of 2D imaging in vivo using animal model systems to explore microwave imaging of therapeutic temperature elevation, thermally-induced lesions and radiation-induced tissue reactions, and (5) refinement and optimization of solid-material array housings for imaging without saline bath immersion. If successful this work would substantially advance the current state-of-the-art in medical microwave imaging technology paving the way for future studies at the clinical scale.